I've two structures and one class in my namespace Dimension. These structures are Dimension.Derived and Dimension.Basis. The class was called Exponent. I had overrided the Function ToString() of my class to get the DisplayNameAttribute of properties in my structure Dimension.Derived.
Public Overrides Function ToString() As String
Dim oType As Type
oType = GetType(Dimension.Derived)
Dim colMemberInfo() As PropertyInfo = oType.GetProperties
For Each oMemberInfo In colMemberInfo
If Me = oMemberInfo.GetValue(oMemberInfo) Then
Dim de As New Dimension.Exponent
de = oMemberInfo.GetValue(oType)
Dim attr() As DisplayNameAttribute = DirectCast(oMemberInfo.GetCustomAttributes(GetType(DisplayNameAttribute), False), DisplayNameAttribute())
If attr.Length > 0 Then
Return attr(0).DisplayName
Else
Exit For
End If
End If
Next
Return Nothing
End Function
That works fine, but it should search through both structures. Therefore, I changed the first lines into
Dim oType1, oType2 As Type
oType1 = GetType(Dimension.Derived)
oType2 = GetType(Dimension.Basis)
Dim colMemberInfo() As PropertyInfo = oType1.GetProperties And oType2.GetProperties
But this throws an exception that the And-Operator is not declared for PropertyInfo. Surely I can repeat the For-Each-loop for the another structure, but that's not the intention. What should I do to merge these PropertyInfos?
And is a boolean operator. It's for True/False values. You want to get a list of PropertyInfo from the two types, so try:
Dim properties as List(Of PropertyInfo) = New List(Of PropertyInfo)
properties.AddRange(oType1.GetProperties())
properties.AddRange(oType2.GetProperties())
Related
I have third party object which contain so many member with integer, string and Boolean. I want to update that record whose value is not null or blank
You can use reflection to achieve what you want:
Sub Main()
Dim obj As Test = new Test()
Dim type As Type = GetType(Test)
Dim info As PropertyInfo() = type.GetProperties()
For Each propertyInfo As PropertyInfo In info
Dim value As String = propertyInfo.GetValue(obj)
If propertyInfo.PropertyType = GetType(String) And String.IsNullOrEmpty(value)
' empty value for this string property
End If
Next
End Sub
public Class Test
Public Property Test As String
End Class
When I get to the Read loop I get an index out of bounds error. I think its on the reader ordinal value, but I am not sure why I am getting it.
Private Function Create(Reader As SqlDataReader) As IEnumerable(Of MyObject)
SetOrdinals(MyObjectReader)
Dim MyObjects = New List(Of MyObject)
While MyObjectReader.Read()
Dim Temp = New MyObject() With {
.FirstValue = MyObjectReader.GetValue(Of Integer)(MyObjectReader(FirstValue_Ord)),
.SecondValue = If(MyObjectReader.GetValue(Of String)(MyObjectReader(SecondValue_Ord)), String.Empty).Trim(),
.ThirdValue = If(MyObjectReader.GetValue(Of String)(MyObjectReader(ThirdValue_Ord)), String.Empty).Trim(),
MyObjects.Add(Temp)
End While
Return MyObjects
End Function
Private Sub SetOrdinals(MyObjectReader As SqlDataReader)
FirstValueOrd = MyObjectReader.GetOrdinal("FirstValue")
SecondValue_Ord = MyObjectReader.GetOrdinal("SecondValue")
ThirdValue_Ord = MyObjectReader.GetOrdinal("ThirdValue")
End Sub
End Class
Public Module Extensions
<Extension>
Function GetValue(Of T)(rdr As SqlDataReader, i As Integer) As T
If rdr.IsDBNull(i) Then
Return Nothing
End If
Return DirectCast(rdr.GetValue(i), T)
End Function
End Module
You should just be passing in the ordinal to the GetValue calls:
While MyObjectReader.Read()
Dim Temp = New MyObject() With {
.FirstValue = MyObjectReader.GetValue(Of Integer)(FirstValue_Ord),
.SecondValue = If(MyObjectReader.GetValue(Of String)(SecondValue_Ord), String.Empty).Trim(),
.ThirdValue = If(MyObjectReader.GetValue(Of String)(ThirdValue_Ord), String.Empty).Trim()
}
MyObjects.Add(Temp)
End While
Here my version :)
Private Function Create(reader As SqlDataReader) As IEnumerable(Of MyObject)
Dim objects As New List(Of MyObject)()
Dim ordinals As New Ordinals(reader)
While reader.Read()
Dim Temp As New MyObject With
{
.FirstValue = reader.GetValueOrDefault(Of Integer)(ordinals.FirstValue),
.SecondValue = reader.GetValueOrDefault(ordinals.SecondValue, "").Trim(),
.ThirdValue = reader.GetValueOrDefault(ordinals.ThirdValue, "").Trim()
}
objects.Add(Temp)
End While
Return MyObjects
End Function
Private Class Ordinals
Public Property FirstValue As Integer
Public Property SecondValue As Integer
Public Property ThirdValue As Integer
Public Sub New(reader As SqlDataReader)
FirstValue = reader.GetOrdinal(nameOf(FirstValue))
SecondValue = reader.GetOrdinal(nameOf(SecondValue))
ThirdValue = reader.GetOrdinal(nameOf(ThirdValue))
End Sub
End Class
Public Module Extensions
<Extension>
Function GetValueOrDefault(Of T)(reader As SqlDataReader, ordinal As Integer) As T
Return reader.GetValueOrDefault(Of T)(ordinal, Nothing)
End Function
<Extension>
Function GetValueOrDefault(Of T)(reader As SqlDataReader,
ordinal As Integer,
defaultValue As T) As T
Dim value = reader(ordinal)
If value = DbNull.Value Then
Return defaultValue
End If
Return DirectCast(value, T)
End Function
End Module
Because extension method execute checking for DbNull.Value against already extracted object, we get rid from reading same value twice from SqlDataReader.
SqlDataReader.IsDbNull(index) reads value before checking for DbNull.
Extension method have two overloads:
- One which return default value of given type, if value is DbNull.Value. Nothing in vb.net is default value of type.
- And one which takes parameter for default value you want return if value is DbNull.Value. Possibility pass default value makes lines where you create new object shorter and more readable. We get rid of inline if statement.
Your extension method with name GetValue have "side effects". By name consumer of this method expect to get value from SqlDataReader. So he can expect to get DbNull.Value if database query return NULL, but instead he get null for string or 0 for integer. Name GetValueOrDefault is little bid more informative, so you don't need to go inside method to check what is doing.
I'm using Entity Framework 6.0, DbContext. I'm using this method to copy an object and some related children:
Imports System.Data.Objects
Imports System.Data.Objects.DataClasses
Imports System.Runtime.CompilerServices
Public Module Entities
<Extension()>
Public Function CloneEntity(Of T As Class)(entity As T, context As ObjectContext, Optional include As List(Of IncludeEntity) = Nothing, Optional copyKeys As Boolean = False) As T
Return CloneEntityHelper(entity, context, include, copyKeys)
End Function
Private Function CloneEntityHelper(Of T As Class)(entity As T, context As ObjectContext, Optional include As List(Of IncludeEntity) = Nothing, Optional copyKeys As Boolean = False) As T
If include Is Nothing Then include = New List(Of IncludeEntity)()
Dim myType = entity.GetType()
Dim methodInfo = context.GetType().GetMethod("CreateObject").MakeGenericMethod(myType)
Dim result = methodInfo.Invoke(context, Nothing)
Dim propertyInfo = entity.GetType().GetProperties()
For Each info In propertyInfo
Dim attributes = info.GetCustomAttributes(GetType(EdmScalarPropertyAttribute), False).ToList()
For Each attr As EdmScalarPropertyAttribute In attributes
If (Not copyKeys) AndAlso attr.EntityKeyProperty
Continue For
End If
info.SetValue(result, info.GetValue(entity, Nothing), Nothing)
Next
If info.PropertyType.Name.Equals("EntityCollection`1", StringComparison.OrdinalIgnoreCase) Then
Dim shouldInclude = include.SingleOrDefault(Function(i) i.Name.Equals(info.Name, StringComparison.OrdinalIgnoreCase))
If shouldInclude Is Nothing Then Continue For
Dim relatedChildren = info.GetValue(entity, Nothing)
Dim propertyType As Type = relatedChildren.GetType().GetGenericArguments().First()
Dim genericType As Type = GetType(EntityCollection(Of ))
Dim boundType = genericType.MakeGenericType(propertyType)
Dim children = Activator.CreateInstance(boundType)
For Each child In relatedChildren
Dim cloneChild = CloneEntityHelper(child, context, shouldInclude.Children, shouldInclude.CopyKeys)
children.Add(cloneChild)
Next
info.SetValue(result, children, Nothing)
End If
Next
Return result
End Function
Public Class IncludeEntity
Public Property Name As String
Public Property Children As New List(Of IncludeEntity)
Public Property CopyKeys As Boolean
Public Sub New(propertyName As String, ParamArray childNodes() As String)
Name = propertyName
Children = childNodes.Select(Function(n) new IncludeEntity(n)).ToList()
End Sub
End Class
End Module
Now I'm using the code like below :
Dim litm, newitm As New MyObject
Dim inc = New List(Of IncludeEntity)()
inc.Add(New IncludeEntity("Child_list"))
litm=context.MyObjects.FirstOrDefault
newitm = litm.CloneEntity(CType(context, Entity.Infrastructure.IObjectContextAdapter).ObjectContext,include:=inc)
The code is executed without errors, but nothing is copied, so newitm is empty.
I have inspected the code and found that this line on the CloneEntity function :
Dim myType = entity.GetType()
Is producing a strange type.
I'm expecting that the type will be of MyObject type, but instead this return :
MyObject_F2FFE64DA472EB2B2BDF7E143DE887D3845AD9D1731FD3107937062AC0C2E4BB
This line too :
Dim result = methodInfo.Invoke(context, Nothing)
produces the same strange type.
I don't know if this is the problem, but this is the only strange thing I have noticed.
Can you help me to find out why this code doesn't work?
Thank you!
Entity framework, like many other ORMs will build a proxy type for your entities so that it can intercept calls to:
Lazy load the contents of any collection contained as properties within your entity, when you access those collection properties.
Detect that you have made changes to the properties of an instance as part of dirty checking, so that it will know which objects are dirty and need to be saved to the database when you invoke SaveChanges.
Refer for example to EF returning proxy class instead of actual entity or Working with Proxies.
If you want to find out the underlying type of your entity that is wrapped by the proxy, i.e. the one that would match with the type you are looking for (e.g. MyObject), you can do that using a method in the object context:
var underlyingType = ObjectContext.GetObjectType(entity.GetType());
I'm working up a system where I plan on using RealProxy objects to enable intercepting method calls against a set of objects, handling the call, and then returning appropriate results.
This works just find for simple return types like strings or ints, but I can't seem to return objects from the RealProxy.Invoke method.
Everything works. I get no errors, but the returned value is always NOTHING, instead of an object.
I've worked up the smallest sample code I could, and have included it below.
Essentially, just call RPtest and single step through.
The code creates a simple object, RPTestA, with a string field and an object valued field
It then retrieves the string
Dim x = c.Name
Which works fine
and then attempts to retrieve the object
Dim r = c.SubObj
Which always returns nothing.
However, in the FieldGetter routine, this code:
'---- the field is an OBJECT type field
Dim mc = New MethodCallMessageWrapper(Msg)
'---- create the object
Dim o = Activator.CreateInstance(t)
'---- and construct the return message with that object
Dim r = New ReturnMessage(o, mc.Args, mc.Args.Length, mc.LogicalCallContext, mc)
Return r
appears to work just fine, setting the ReturnValue field of the ReturnMessage to the object that was created by the Activator.CreateInstance(t) call just above.
I suspect it's a serialization thing of some sort, but I'm at a loss.
You should be able to run this code straight away, but just pasting it into a new VB.net project.
'----------------------------------------------------------------------------
Imports System.Security.Permissions
Imports System.Diagnostics
Imports System.Reflection
Imports System.Runtime.CompilerServices
Imports System.Runtime.Serialization
Imports System.Runtime.Remoting
Imports System.Runtime.Remoting.Activation
Imports System.Runtime.Remoting.Messaging
Imports System.Runtime.Remoting.Proxies
Public Module RPTest
Public Sub RPTest()
'---- create a new object that is automatically proxied
' See the RPProxyAttribute for details
Dim c = New RPTestA
Dim x = c.Name
'x is returned as a string value just fine
Dim r = c.SubObj
'********* PROBLEM IS HERE, r ends up nothing
End Sub
End Module
'ROOT test object
Public Class RPTestA
Inherits RPBase
Public Name As String = "Test Name"
Public SubObj As RPTestB
End Class
'SUB OBJECT which should be returned as a field value from the root object above
Public Class RPTestB
Inherits RPBase
Public SubProperty As String = "SubObj Test Property"
End Class
''' <summary>
''' Base proxyable object class
''' </summary>
''' <remarks></remarks>
<RPProxy()> _
Public MustInherit Class RPBase
Inherits ContextBoundObject
End Class
<PermissionSet(SecurityAction.Demand, Name:="FullTrust")> _
Public Class RPProxy
Inherits RealProxy
Private m_target As MarshalByRefObject
Public Sub New()
m_target = DirectCast(Activator.CreateInstance(GetType(ConfigRP)), MarshalByRefObject)
Dim myObjRef = RemotingServices.Marshal(m_target)
End Sub
Public Sub New(ByVal classToProxy As Type)
MyBase.New(classToProxy)
End Sub
Public Sub New(ByVal ClassToProxy As Type, ByVal targetObject As MarshalByRefObject)
m_target = targetObject
Dim myObjRef = RemotingServices.Marshal(m_target)
End Sub
Public Overrides Function Invoke(ByVal msg As IMessage) As IMessage
Dim returnMsg As IMethodReturnMessage = Nothing
If TypeOf msg Is IConstructionCallMessage Then
'---- handle constructor calls
Dim ConstructionCallMessage = DirectCast(msg, IConstructionCallMessage)
returnMsg = InitializeServerObject(ConstructionCallMessage)
Me.m_target = Me.GetUnwrappedServer()
SetStubData(Me, Me.m_target)
Return returnMsg
ElseIf TypeOf msg Is IMethodCallMessage Then
'---- handle all other method calls
Dim methodCallMessage = DirectCast(msg, IMethodCallMessage)
'---- before message processing
preprocess(methodCallMessage)
'---- execute the method call
Dim rawReturnMessage = RemotingServices.ExecuteMessage(Me.m_target, methodCallMessage)
'---- and postprocess
returnMsg = postprocess(methodCallMessage, rawReturnMessage)
Else
Throw New NotSupportedException()
End If
Return returnMsg
End Function
'Called BEFORE the actual method is invoked
Private Sub PreProcess(ByVal msg As IMessage)
Console.WriteLine("before method call...")
End Sub
'Called AFTER the actual method is invoked
Private Function PostProcess(ByVal Msg As IMethodCallMessage, ByVal msgReturn As ReturnMessage) As ReturnMessage
Dim r As ReturnMessage
If Msg.MethodName = "FieldGetter" Then
r = FieldGetter(Msg, msgReturn)
ElseIf Msg.MethodName = "FieldSetter" Then
'na
r = msgReturn
ElseIf Msg.MethodName.StartsWith("get_") Then
'na
r = msgReturn
ElseIf Msg.MethodName.StartsWith("set_") Then
'na
r = msgReturn
Else
r = msgReturn
End If
Return r
End Function
Private Function FieldGetter(ByVal Msg As IMethodCallMessage, ByVal msgReturn As IMethodReturnMessage) As IMethodReturnMessage
Dim t = Me.Target.GetType
'---- This retrieves the type of the field that the getter should retrieve
t = t.GetField(Msg.InArgs(1), BindingFlags.Instance Or BindingFlags.Public).FieldType
If t.Name = "String" Then
'---- just return what the object returned as a result of ExecuteMessage
Return msgReturn
ElseIf t.BaseType.Equals(GetType(RPBase)) Then
'---- the field is an OBJECT type field
Dim mc = New MethodCallMessageWrapper(Msg)
'---- create the object
Dim o = Activator.CreateInstance(t)
'---- and construct the return message with that object
Dim r = New ReturnMessage(o, mc.Args, mc.Args.Length, mc.LogicalCallContext, mc)
Return r
Else
Return msgReturn
End If
End Function
Public Property Target() As Object
Get
Return Me.m_target
End Get
Set(ByVal value As Object)
Me.m_target = value
End Set
End Property
End Class
<AttributeUsage(AttributeTargets.Class)> _
<SecurityPermissionAttribute(SecurityAction.Demand, Flags:=SecurityPermissionFlag.Infrastructure)> _
Public Class RPProxyAttribute
Inherits ProxyAttribute
Public Overrides Function CreateInstance(ByVal Type As Type) As MarshalByRefObject
Dim proxy = New RPProxy(Type)
Dim transparentProxy = DirectCast(proxy.GetTransparentProxy(), MarshalByRefObject)
Return transparentProxy
End Function
End Class
Well, it turns out to be a pretty simple fix, once you work past the god awful ReturnMessage constructor that's quite misleading!
Many thanks to an old colleague of mine, Rich Quackenbush, for taking a few minutes and checking this out. Sometimes, you can't see the forest for the trees!
Anyway, in FieldGetter, I was doing this
ElseIf t.BaseType.Equals(GetType(RPBase)) Then
'---- the field is an OBJECT type field
Dim mc = New MethodCallMessageWrapper(Msg)
'---- create the object
Dim o = Activator.CreateInstance(t)
'---- and construct the return message with that object
Dim r = New ReturnMessage(o, mc.Args, mc.Args.Length, mc.LogicalCallContext, mc)
Return r
Seems completely reasonable, that newly created object being passed into the ReturnMessage constructor argument called ReturnValue.
But no. You actually have to create an object array and pass it is as the 3 element in that array, like this:
ElseIf t.BaseType.Equals(GetType(RPBase)) Then
'---- the field is an OBJECT type field
Dim mc = New MethodCallMessageWrapper(Msg) '---- create the object
Dim o = Activator.CreateInstance(t)
'---- and construct the return message with that object
Dim r = New ReturnMessage(Nothing, New Object() {Nothing, Nothing, o}, 3, mc.LogicalCallContext, mc)
Return r
It turns out, this is because the FieldGetter function is what in being "called" and intercepted by the proxy, and it's signature is
FieldGetter(StringtypeName,StringfieldName,Object&val)
Which, for purposes of constructing a ReturnMessage for that call means that it doesn't have a Returnvalue at all, but rather that the return value is returned as the 3'rd argument in that list.
Since I'm not actually calling the real FieldGetter function, the first two argument (the typename and fieldname) are immaterial, but that 3'rd argument is the proper place to put the return value.
It's always obvious in hindsight!
Many thanks to Rich.
What I want to do is, based on the type of T do different opperations. Below is a simple example of my problem.
Public Shared Function Example(Of T)() As T
Dim retval As T
If TypeOf retval Is String Then
Dim myString As String = "Hello"
retval = myString
ElseIf TypeOf retval Is Integer Then
Dim myInt As Integer = 101
retval = myInt
End If
Return retval
End Function
I get the error "Value of Type 'String' Cannot be converted to 'T'" Same with the integer part. If I cast either to an object before asigning them to retval it works but I think that would defeat my purpose and be less efficient. Any Ideas? Thanks!
It's probably a bit late, but try this:
Public Shared Function CAnyType(Of T)(ByRef UTO As Object) As T
Return CType(UTO, T)
End Function
Public Shared Function ExecuteSQLstmtScalar(Of T)(ByVal strSQL As String) As T
Dim T_ReturnValue As T
' Here we have the result of a DB query '
Dim obj As Object = "Value from DB query cmd.ExecuteScalar"
Dim strReturnValue As Object = obj.ToString();
Try
Dim tReturnType As Type = GetType(T)
If tReturnType Is GetType(String) Then
Return CAnyType(Of T)(strReturnValue)
ElseIf tReturnType Is GetType(Boolean) Then
Dim bReturnValue As Boolean = Boolean.Parse(strReturnValue)
Return CAnyType(Of T)(bReturnValue)
ElseIf tReturnType Is GetType(Integer) Then
Dim iReturnValue As Integer = Integer.Parse(strReturnValue)
Return CAnyType(Of T)(iReturnValue)
ElseIf tReturnType Is GetType(Long) Then
Dim lngReturnValue As Long = Long.Parse(strReturnValue)
Return CAnyType(Of T)(lngReturnValue)
Else
MsgBox("ExecuteSQLstmtScalar(Of T): This type is not yet defined.")
End If
Catch ex As Exception
End Try
Return Nothing
End Function
(the secrect is casting your generic result to object, then casting from type Object to template type T).
PS:
You are responsible to ensure that your code works correctly with nullable types and NOT nullable types, as well as System.DbNull.Value. For example when string is NULL and return value type is Boolean (not nullable). On a sidenote, please also note that VB Nothing is NOT equal NULL, it's equal to C#'s default(T) (e.g. System.Guid.Empty for Guid)
With a generic method, T will be of exactly one type each time. Let's say that you have code calling Example(Of Integer). Now, in your mind, replace T with Integer. The resulting method will contain these lines (amongst others).
Dim retval As Integer
If TypeOf retval Is String Then
Dim myString As String = "Hello"
retval = myString
' more code follows '
Assigning a String to an integer like that will never work. Sure, that code will also never execute, since the If-block prevents that, but the code will still not compile. (As a side not, the above code will fail to compile because the TypeOf keyword is restricted to use with reference types, but that is another story)
Typically when creating generic methods, you will want to do the same thing with whatever input you get, but in a type safe manner. If you want to have different behavior for different types of input, you are usually better off by overloading the methods instead.
retVal = (T) "Hello World!"
Do retval = Ctype(Mystring, T) or retVal = Ctype(MyInt, T)
An alternative solution is encapsulate this kind of logic in a class and use VB CallByName function:
Class Aux(Of T)
Public Value As T
Private dicc As Dictionary(Of String, Object)
Sub New()
dicc = New Dictionary(Of String, Object)
dicc.Add("system.string", "hola")
dicc.Add("system.int32", 15)
dicc.Add("system.double", 15.0)
End Sub
Public Function Test() As T
Dim typeName As String = GetType(T).ToString.ToLower
If dicc.ContainsKey(typeName) Then
CallByName(Me, "Value", CallType.Set, dicc(typeName))
End If
Return Value
End Function
Protected Overrides Sub Finalize()
MyBase.Finalize()
If Not (dicc Is Nothing) Then dicc.Clear()
dicc = Nothing
End Sub
End Class